NP-FW50 Weight - varies

Hi, I reckon weight is a good way to tell. The life of the battery is likely to be less than the real Sony battery (around 60% or so), and there may be compatibility issues between it and current/future bodies.

Some of the fakes come in very convincing "Sony" packaging, including an instruction leaflet. I got sold one of these, and was able to tell by the weight and battery life that the battery wasn't right. The seller refunded the money without a quibble when this was pointed out.

My guess is that the 42g battery is most likely a fake. The other 2 are I guess OK.